Sulfur is the fourth important element for the growth of crops, the importance of which is only smaller than that of the three basic mineral elements. The main effect of sulfur includes: 1) sulfur is a component of three sulfur-containing amino acids in the plants (i.e. cysteine, cysteine and methionine), which determines the amount, quality and functions of proteins in the plant and influences the structure of the cellular protoplasm, cold and dry resistances of the plant as well as the quality of the crops, etc. Sulfur is involved in the synthesis of the chlorophyll in plants as well as some important metabolism polymer compounds, such as enzyme, coenzyme A, vitamin H and vitamin B. 2) Sulfur plays an important role in various important metabolism processes in cells of the plant. For example, sulfur transfers electrons during the photosynthesis and the reduction of oxides like nitrite; and sulfur improves nitrogen metabolism and supply of sugar during a process of biological nitrogen fixation, which facilitates the nitrogen fixing effect of rhizobium and azotobacter. During the absorption of nutrients, sulfur influences the absorption of other elements in the plant via an antagonistic action or a synergism. 3) The fragrant and pungent smells as well as toxicity of certain plants are all related to sulfur-containing compounds. To some extent, sulfur can provide the plant with self-protection, and prevent the plant from the attacks of insects and animals. It is reported that, glutathione and nonprotein hydrosulfide may be the main components in the plant which are capable of removing the damage from heavy metal chromium. The above-mentioned components all contain element sulfur, therefore sulfur also has the function of detoxication.
Sulfur is essential to the growth and metabolism of the plant. Due to the high centralization of agriculture, the removal of large amount of nutrients per unit area as well as the increase application of high-density sulfur-free fertilizer, however, the lack of sulfur in the soil is becoming increasingly serious. Therefore it is urgent to use sulfur fertilizers. According to a series of latest practical tests which applies sulfur fertilizer based on the application of nitrogen fertilizer, it is indicated that the sulfur fertilizer may increase the yield of plant, improve the quality of soil, keep the plant healthy, improve the quality of the crops and increase the utility of other nutrients.
Currently, a common sulfur-containing fertilizer includes ammonium sulfate, potassium sulfate, potassium magnesium sulfate, and superphosphate. However, the utilization rate of element sulfur in these sulfur-containing fertilizers is low. In connection with the practical requirements of agricultural production and environmental protection, there is more and more research on environmental fertilizer containing higher amounts of sulfur. Nowadays, there are a lot of slow and controlled release fertilizers which apply sulfur on the outer surface of particles of the fertilizer, among which urea is the most common one. However, the sulfur coatings applied on the particles of urea are easy to fall off. In addition, the sealing agent and modifying agent are both hard to absorb by the plant.
Therefore, there is still a need for further modifying fertilizer containing sulfur.